1. Field of the Invention:
This invention relates generally to devices for skimming oil from the surface of water.
More specifically, this invention relates to a dual drum skimmer having a very high oil pick-up rate and adapted for operation in extremely shallow and in trash-laden water.
2. Description of Related Art:
Spills of hydrocarbons into bodies of water are a common occurrence during the production of crude oil and the transport of crude oil and of refined hydrocarbon products. Ordinarily, efforts are made to limit the spread of the spilled hydrocarbons by encircling the spill area with booms and to then recover as much of the hydrocarbon liquids as is possible using a variety of skimming devices such as weir skimmers, disc skimmers, and mop skimmers.
A weir skimmer typically comprises a barrier wall of adjustable height which allows oil floating on water to flow over the wall and into a collection trough while excluding water. Recovered oil is then continuously pumped from the collection trough to a storage or transport means. Weir skimmers operate well in calm water with large or contained spills which produce a relatively thick oil layer.
Disc skimmers ordinarily include a plurality of discs spaced apart coaxially along a rotating shaft which is supported by floats to position the lower portion of the discs in the water. Oil contacts and adheres to the rotating discs and is removed by blades or wipers which direct the collected oil into a sump or other collection means.
A mop skimmer, or rope skimmer, is arranged to contact the oil film with an absorbent or filamentous member to which the oil clings. The oil-heavy member is then passed between rollers which squeeze out and collect the oil.
Those various skimming devices are ordinarily employed on spills occurring in open water. Spills on land, where liquid hydrocarbons often end up in small streams, drainage ditches, and the like present very different problems. Water bodies which are contaminated by land spills typically are shallow and usually are trash covered. The skimmers of traditional design have limited use at best in such circumstances and are seldom employed. Rather, use is made of absorbents to soak up oily liquids and of vacuum trucks to pick up oils from the water surface by suction means. Use of absorbents results in the production of large volumes of oily wastes which require disposal while vacuum collection methods usually results in the collection of large amounts of water with the oil.
Drum skimmers have also been used for the removal of oil and other hydrocarbons from water surfaces. A drum skimmer consists of one or more large rollers, or drums, which rotate partly submerged in water. Oil attaches to the drum surface as the drum rotates through the oil-water interface. The attached oil is then removed by squeezing or scrapping the oil from the drum surface. One early example of such a device is shown in the Schamberger patent, U.S. Pat. No. 1,860,819. The Schamberger device utilizes two closely spaced rollers turning in opposite directions. In operation, the rollers are adjusted to dip beneath the surface of a water channel containing floating oil and are rotated in such a direction as to pull the oil film under the roller. The oil film transfers to the roller surface and is carried around the roller to the back side therof where it is scraped off by a stationary blade and directed into a trough for recovery.
Later, Van Stavern et al. in U.S. Pat. No. 3,612,277, disclosed a tandum drum arrangement in which one drum was partly submerged in water while the second, and smaller, drum was placed above the water surface and at a close, critical spacing from the first drum. Oil picked up by rotation of the first drum was then transferred in part to the second drum. Doctor blades were located on the back side of each drum to scape oil from the drum surfaces and into collection troughs. That arrangement, using one drum or roller to pick up oil from the water surface and the other roller to transfer a portion of the oil from the surface of the first roller to that of the second, was said to have the advantage of reducing the amount of water collected with the oil.
A patent to Thomas, U.S. Pat. No. 4,315,818, describes another type of drum skimmer adapted to pick up heavy fuel oils and the weathered, emulsified residue of an oil spill commonly called "mousse". The Thomas device employs a large pickup drum having corrugations in the form of gear teeth extending across the drum surface. A second, smaller drum having gear teeth meshing with those of the first drum is arranged to drive the larger drum and to squeeze out oil for recovery in a collector positioned beneath the small drum.
Another type of drum skimmer is described in U.S. Pat. No. 4,681,680 to Delons et al. The skimmer includes means for pulling an oil film floating on the surface of water into contact with a rotating drum which is partially immersed in the water. A housing encloses the rear and bottom of the drum and a propeller is located to draw water into the housing and across the bottom of the drum thus continuously transporting an oil film into contact with the drum.
As with the other types of oil skimmers, none of the present drum skimmers known in the art can operate well in shallow water or in water bodies which are trash laden. Other approaches to the collection of oil from water, as for example vacuum suction means, are readily plugged by trash pulled to the suction nozzle.